This section provides background information related to the present disclosure, which is not necessarily prior art.
Air conditioning systems of extended length vehicles often include an auxiliary evaporator assembly at a rear thereof. Flow of refrigerant through an evaporator of the auxiliary, or rear, evaporator assembly is often controlled by a thermal expansion valve (TEV) assembly, which includes a valve at an input side of the evaporator and a sensor bulb at an output side of the evaporator. The valve meters flow of the refrigerant to the evaporator based on the temperature of the refrigerant that has passed through the evaporator, as sensed by the sensor bulb. For example, if the refrigerant sensed by the sensor bulb is above a predetermined temperature, then the valve will remain open to permit additional refrigerant to pass through the rear evaporator, thereby further cooling the evaporator. If the refrigerant is below a predetermined temperature, then the valve will close to prevent the evaporator from becoming over cooled.
Proximate to the evaporator is a rear blower. The blower generates airflow that is directed across the evaporator and into the rear of the passenger cabin. The airflow is cooled as it passes across the evaporator. In some instances, when the rear blower is turned on and cool air is desired, the rear evaporator assembly will initially blow warm air because the valve is closed, thereby restricting flow of refrigerant to the evaporator. The warm airflow continues until the valve is opened, which can take an undesirably long period of time. Initially blowing warm air into the passenger cabin when cool air is desired makes passengers uncomfortable.
The inventor determined that failure of the valve to timely open can be caused by failure of the valve to completely close when only the vehicle's front evaporator assembly is in use; and the rear evaporator assembly is not in use such that the rear blower is not activated. For example, if the valve remains open, refrigerant will flow through the evaporator and to the sensor bulb, thereby cooling the sensor bulb. If the sensor bulb is cooled below the predetermined temperature, the sensor bulb will signal the valve to close. Because the sensor bulb has been cooled below the predetermined temperature, the valve will not open until the sensor bulb warms to a temperature greater than the predetermined temperature. And because the sensor bulb is not exposed to ambient temperature, but is rather concealed in a case of the rear evaporator assembly, or a wall or floor of the vehicle, it often takes an undesirably long period of time for the sensor bulb to warm and the valve to open. In the meantime, rear passengers have to endure warm airflow until the valve opens.